仮面の告白

Missing, extremely new, or very obvious to obtain.

Most likely a reference to the book "Confession to the Mask" written by Yukio Mishima. In the book the protagonist tries to cope with the fact he lives a double life where he needs to hide his homosexuality, true emotions and true desires. It is a reference to how in society we have to wear a mask and can't express our true self. Considering the achievement comes from a memory bubble where Sampo is asked to explain his true feelings it is likely a spot on reference + Sampo is part of the Masked Fools. - Credit: Fen